Etching lithographic plates



To the accomplishment of Patented Jan. 20, 1942 S PATENT OFFICE ETCHIN GIJTHOGRAPHIC PLATES William H. Wood, Bedford, Ohio, assignor toHarris-Seybold-Potter .Company, Cleveland, Ohio, a corporation of OhioNo Drawing. Application April 12, 1940,

, Serial No. 329,343

be used to remove the residue of the developer e e 11 Claims.

In'the manufacture of deep-etch lithographic plates it is customary tocoat a cleaned and counter-etched zinc or aluminum plate with a resistwhich is sensitive to light, and the plate is then exposed to light inthe form of the subject matter'which is to be reproduced, such that inthose areas where no image is desired on the finished plate the resistis hardened; then the unhardened areas of the resist are removed by ,adeveloping agent so as to leave the image portions of the plate clean.-A so-called deepetching solution is then applied to the plate andallowed to attack the exposed image areas until the metal is etched awayto the desired depth, and after drying, the deep etched areas aretreated with material, commonly referred to as a lacquer, to render themreceptive to inlr. Subsequently the light-hardened areas of the resist,which during etching have served to protect the non-image areas of theplate, are re-' moved by a clean-up solution. The plate is then given adesensitizing etch to make the nonlmage areas receptive to water and isready for printing. In accordance with the present invention, improvedprocedure and materials are involved, such as to. afiord more easymanipulation and control, and. more reliable and positive action, andmaking possible the production of remaining on the, plate.

Following removal of the unhardened portions more rapid in its earlystages than is desirable and subsequently diminishes rapidly, thusmaking it difiicult to control accurately the extent of the etchingaction. Such solutions also tend .to preserve or emphasize the roughcharacter of the plate surface. In addition, in the case of such ironchloride solution a portion of the iron chloride may crystallize ,out ormay form plates having improved longevity, definition,

fidelity and uniformity.

the foregoing and related ends, the invention, then, comprises thefeatures hereinafter fully described, and particularly pointed out inthe claims, the following description setting forth in detail certainillustrative embodiments of the invention, these being indicativehowever, of but a few of the various ways in which the principle of theinvention may be employed.

In the preparation of plates in accordance with my invention, I mayemploy any usual or preferred materials, as for instance the well knownglue or gum arabic. Such coating material, suitably sensitized with asuitable dichromate or the like as usual, is app ied to the metal plate,as in the well-known practice.

The coated metal plate, (the metal being usual or as preferred, zinc,aluminum, etc), having been exposed to light and the subject matterwhich is to be reproduced, is treated with the developer, which may beof any usual or pre-- ferred material, for instance a concentratedsolution, about 50 B., of calcium chloride confollowing the developer,anhydrous alcohol may ferric hydroxide or metallic iron, thus leaving adeposit on the plate causing the lacquer to lift where it should adhere.In etching in accordance with the present invention however, I apply asaturated solution of magnesium chloride in water to which has beenadded a small amount, for instance two to five per cent by weight ofeach of two water-soluble monobasic aliphatic acids, viz. formic andglycollic (the latter also known as hydroxyacetic), or formic andhydracrylic acids. Less advantageously, acetic or propionic acid can beused in lieu of formic acid in some cases. This etching material resultsin certain new and difierentefiects distinguished by the followingcharacteristics: (1) it has the effect of smoothing out the grain of theetched of the roughened surface to a greater extent than from thevalleys; (2) it has a slower and more moderate action than previouslyknown etching solutions, requiring a longer time, such as one andone-half to three minutes, for the completion of a suitable degree ofetching, and is therefore more easy to control; (3) it maintains itsetching activity for a longer period and etching continues throughoutthe extent of the time required in normal operation. This deep-etchingmaterial may be used on aluminum as well as on zinc, but for bestresults on aluminum plates it is desirable to include ferric chloride,as in amount of five to twenty per cent in substitution for equivalentamounts of the magnesium chloride.

Having etched the plate by the usual or the preferred etching materialsas indicated, the hardened resist is next removed from the nonimageareas of the plate which it has protected during the deep-etching, andfor this, I prefer to employ a water solution of gluconic acid, forinstance about one to five per cent. Gluconic acid is novel in thisrelation, and is very useful with known resists, but is particularlydesirable where the preferred resists as above described have beenemployed.

This application is a continuation, in part and as to common subjectmatter, of my application Serial No. 223,523, filed August 6, 1938.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims, or the equivalent ofsuch, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In a process of making lithographic plates, etching the developedplate with a saturated solution of magnesium chloride containing two tofive per cent by weight each of formic and glycollic acid.

2. In a process of making lithographic plates,

etching the developed plate witha solution of magnesium chloridecontaining formic and glycollic acid.

3. In a process of making lithographic plates,

etching the developed plate with a saturated solution of magnesiumchloride containing a small per cent of a water-soluble monobasicaliphatic acid. I 4. In a process of making lithographic plates, etchinga developed aluminum plate with a solution of magnesium chloride andferric chloride, containing formic and glycollic acids in amount two tofive per cent each.

5. Ina process of making lithographic plates, etching a developedaluminum plate with a solution of magnesium chloride and ferricchloride,

containing formic and glycollic acids.

6. In a process of making lithographic plates,

etching a developed aluminum plate with a solution of magnesium chlorideand ferric chloride, containing a small per cent of a water-solublemonobasic aliphatic acid.

7. In a process of making lithographic plates, etching the developedplatewith a saturated solution of magnesium chloride containing two tofive per cent by weight each of formic and glycollic acid, and thentreating the plate with a one to five per cent water solution ofgluconic acid.

8. In a process of making lithographic plates, etching the developedplate with a solution of magnesium chloride containing formic andglycollic acid, and then treating the plate with a one to five per centwater solution of gluconic acid.

9. In a process of making lithographic plates, etching the developedplate with a saturated solution of magnesium chloride containing a smallper centof a water-soluble monobasic aliphatic acid, and then treatingthe plate with a one to five per cent water solution of gluconic acid.

10. In a process of making lithographic plates, etching a developedaluminum plate with a solution of magnesium chloride and ferricchloride, containing formic and glycollic acids in amount two to fiveper cent each, and then treating the plate with a one to five ofgluconic acid.

11. In a process of making lithographic plates, etching a developedplate, and then treating the plate with a solution of gluconic acid.

WILLIAM H. WOOD.

per cent water solution;

